When I am in a low gear (1st or 2nd) and abruptly close the throttle (i.e. get a lot of engine braking), a sharp loud squeak will elicit from the rear of the car. The squeak happens in phase with each forward pitch of the car as the car's pitching motion is quickly decayed by the dampers. The squeak's severity also decays as the pitching motion is damped out. Did that make sense?

I also hear the squeak consistently when I use the brakes moderately, but NOT when I clamp down hard on the brake pedal.

Seems to be related to rear suspension travel (extension) then. But I don't hear the squeak while driving over deep ruts or bumps or other things that compress/extend the rear wheels individually. I guess it only happens if both rear wheels get extended simultaneously.

What could cause this? Worn universal joint? Worn torque rod bushings? I'm new to live axles (and 240s for that matter!)... where to look?